Technical lignins are natural and renewable poly-phenolic polymers obtained mainly as a byproduct from the pulp industry. They present a complex structure that depends on the wood type and the pulping process adopted to separate cellulose. Nowadays, lignins are used as partial replacement of phenol (P) –a non renewable resource, expensive and toxic- in the formulation of phenolic resins (PF). However, lignins must be chemically modified to increase their reactivity toward formaldehyde (F). In the literature there is a lot of information about the use of PF resins modified with lignins (LPF) as adhesives for the production of wood-based composites. However, the use of LPF resols for paper impregnation to obtain high pressure laminates (HPL) has been scarcely studied. A HPL comprises a decorative paper-based surface and a substrate of Kraft-type papers impregnated with PF resins. In this work, commercial hardwood (sodium lignosulfonate and Kraft-type) lignins were modified by hydroxymethylation and used to replace P in PF resins. The LPF resins were employed to produce HPL. The work involved: i) the modification of lignins by hydroxymethylation at different temperatures (40, 50 and 70 ○C) and pHs (9 and 12), ii) the characterization of lignins and hydroxymethylated lignins by volumetric, gravimetric, spectroscopic and chromatographic techniques; iii) the development of a mathematical model of the hydroxymetylation of sodium lignosulfonate and the estimation of the associated kinetic constants; iv) the synthesis of industrial (conventional and modified) PF resins by replacement of 10, 20 and 30%w/w of P, v) the production and characterization of (laboratory and industrial) HPL including dynamic mechanical analysis to compare conditions of curing and the measurement of tensile modulus, bending strength, biaxial flexural impact strength and Mode-I interlaminar fracture toughness in both processing directions to evaluate the mechanical performance. The optimal conditions of hydroxymethylation were 50 ○C and pH=9. Simulations were in accordance with experimental measurements. All resins (conventional and modified) had similar final properties. The best curing conditions were 70 kg/cm2 and 150 ○C. Also, it was shown that the higher the lignin content, the less crosslinking of the resins. Finally, modified laminates exhibited mechanical properties comparable with those of conventional laminates, indicating a negligible depreciation of them.

Technical lignins modified by hydroxymethylation for the production of high pressure laminates: Synthesis, characterization and mathematical modelling

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.